From Volume Splatting to Raycasting - A Smooth Transition

Splatting-based methods are well suited to render large hierarchical structured or unstructured point-based volumetric datasets. However, as for most object-order volume rendering methods, one major problem still remains the processing of huge amounts of elements usually necessary to represent highly detailed densely sampled datasets, which can lead to poor performances. Resampling into 3D textures to apply hardware-based raycasting is a common way of improving framerate in such cases but often with a certain precision loss related to limited texture memory. Switching between these two rendering techniques is interesting in order to keep the advantages of both and has thus been proposed before, but not in a smooth and hierarchical manner. In this paper, we show that for most point-based volumetric datasets, some parts of the model can be rendered more efficiently with a texture-based method, whereas other parts can be rendered as usual using splatting. We address the issue of providing a smooth hierarchical transition between the two methods using a data-dependent approach based on a per-pixel ray-driven rendering scheme. In practice, our transition scheme allows users a good control of the performance/quality trade-off. Through a comparison with standard hierarchical EWA splatting, we show that our smooth transition can lead to an improvement of framerate without introducing visual inconsistencies or artifacts.